Enzymes catalyze chemical reactions with high specificity and tremendous rate enhancement thus providing a great opportunity for clean industrial productions and efficient biocatalytic conversions. Enzymes with low substrate specificity, too, may attract interest for manifold biotechnological applications. Laccase, indeed, are very versatile enzymes, being able to oxidize an extensive list of aromatic compounds containing hydroxy or amino groups, including pesticides, polycyclic aromatic hydrocarbons and dyes. These properties make laccases good candidates for applications in the pulp and paper industry, textile industry, biosensor development, bioremediation of polluted water and soil. Laccases (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) were discovered in plants, then have been described in fungi, insects and, more recently, in prokaryotes; laccases are thought to be nearly ubiquitous among fungi, where they are usually produced in multiple isoforms as extracellular proteins. The cultural broth of laccase-producing fungi contains generally a main laccase and a number of isoforms some of which closely related, others differing for structural and catalytic properties. The production of different isoenzymes is due to the occurrence of multiple laccase genes in fungi; it is known that the expression of some of these genes is regulated by the presence in the cultures of specific inducers such as copper, ferulic acid 2,5-xylidine. Most fungal laccases are monomeric glycoproteins with molecular masses of about 60,000 Da; they belong to the family of the multi-copper oxidases and catalyze the one-electron oxidation of a large variety of substrates coupled with the reduction of dioxygen to two molecules of water. In the blue laccases, the redox process is brought about by four copper ions arranged in three different centres and coordinated mainly by histidine and cysteine residues and, accordingly to the origin of the enzyme, by leucine or phenylalanine residues. Laccases produced by basidiomycetes show usually a high redox potential (up to about 800 mV), while the enzymes from ascomycetes present lower redox potentials. In recent years, the three-dimensional structure of some laccases has been reported: the comparative analysis of these structures suggested the presence of several conserved or semi-conserved residues and peptides, involved in copper-ligation, interactions with substrates and products, and structured traits. These studies allowed to carry out site-specific mutagenesis studies with the aim to produce engineered enzymes with catalytic properties more useful for specific technological applications.